8/14/2019 Straight talk with Karen Scrivener on cements, CO2 and sustainable development

1/447American Ceramic Society Bulletin, Vol. 91, No. 5 | www.ceramics.org

Straight talk with Karen Scriveneron cements, CO2and sustainable

development

Question:The production

of cement and concretehas been associated with the genera-

tion of a large percentage of the car-bon dioxide emissions in the world.

Should the world be trying to developan alternative construction material?

Scrivener:A lot of people say, Oh, we shouldnt

use concrete. We should be using something else.This is a totally meaningless comment, because it

is just not physically possible to produce any other

material in such large quantities. Thats because ofthe distribution of resources on Earth. This to me is areally key point.

Concrete is the most used material in the world.Looking forward, especially to the developing regions

of the world, it is the only material that can satisfythe demand for decent low-cost housing and infra-

structure. Also, concrete is relatively environmentallyfriendly as measured by CO

2emissions per ton, which

is lower than wood.But, its wrong to think there is or could be some

competition with wood. The usage of wood world-wide is estimated to be well above replanting levels,

so we cannot substantially increase the amount ofwood used. Also, while it may be a viable material in

temperate climes, in large parts of Africa, India andAsia, there are no significant reserves. There is no

way for the Earth to produce enough wood to make

any significant replacement of concrete.Q:So, you are saying there really is no viable

alternative to concrete?A:Yes, and if you use any alternative to concrete,

you are going to make things worse. Therefore, theonly route we have is to make concrete better.

Q:Is part of the problem that people in the devel-oped countries dont grasp what role concrete plays

Editors note: Over the last few years, I have run into a chorus of stories

in both the technical and mainstream press bemoaning the carbon diox-

ide emissions of the cement and concrete industries. It seemed that the

accepted wisdom was that something was amiss, and the implication

was that cement and concrete production needed, well, to be fixed.

It was a revelation, then, last year when I met Karen Scrivener, a profes-

sor at the Swiss Ecole Polytechnique Federale (Lausanne) who was

delivering the Della Roy Lecture at the 2011 Advances in Cement-based

Materials: Characterization, Processing, Modeling and Sensing meeting. I

learned first hand that Scrivener, a founder of a Europe-based collabora-

tion between institutions and industry focusing on strategic problems

(Nanocem), is a dynamic and articulate expert on cement and concrete.

More importantly for me, she was the first person I have heard present

an aggressive, well-rounded and compelling defense of the critical

role of concrete and at the same time sketch out a realistic set of

pathways for materials scientists and engineers to reduce cements CO2footprint while increasing concretes availability. Read our Q&A and see

if you agree.

- Peter Wray

c o v e r s t o r ybulletin

Concrete: The most used material in the world . . .

. . . and the only material which can satisfy the demand for decent

housing and infrastructure.

8/14/2019 Straight talk with Karen Scrivener on cements, CO2 and sustainable development

2/448 www.ceramics.org | American Ceramic Society Bulletin, Vol. 91, No. 5

Straight talk with Karen Scrivener on cements, CO2and sustainable development

in the underdeveloped regions of the

world?A:I think so. We all want to have

a place to live. We all want to have aroad to drive on. And, the only way

we can meet these demands is by usingmore concrete. The real question is,

how do we fill the needs of a grow-ing world population that is becoming

more and more urbanized? We may not

like that, but its a fact, and we have todeal with it. We cant afford to be likeostriches and stick our head in the sand

and pretend this growth is not happen-ing. It is happening.

Obviously, the problem is thatCO

2doesnt just stay in one place. It

doesnt stay in China or Africa. It goeseverywhere, so we have to have a more

holistic approach in tackling this prob-lem. Wherever you are, concrete is the

most accessible and least environmen-

tally damaging material.Q:But, we even hear our colleagues

in the materials community long for analternative to the Portland cement used

to make concrete.A:Yes, even after my lecture at the

ACerSACBM meeting last year, Iheard that someone in the audience

suggested that some science funders inthe United State think we should give

up on Portland cement. Thats ludi-crous, because, like it or not, Portland

cement is the most viable formulation

of cement. Its not by coincidence thatwe have ended up with this formula-

tion, because it is based on years ofexperience of what are the most widely

available materials.Now, I think we have to look at

using other materials to substitutefor some of the Portland cement, but

it doesnt help to think that we cansimply throw it away and start with

something new. If you want to look atsomething else, then you have to start

looking at materials that are not widelyavailable and that have hugely differ-

ent cost structures, and you will quicklyfind yourself in the same raw materials

dilemma where the materials neededare only available in some countries but

not others. It would be like the situa-tion with rare earths.

Q:Every so often we see an

announcement about a new low-CO2

cement. Are you saying these arentviable?

A:Well, let me first say that many

of them do work and some of themdont work. But, even if they all

worked, it would be a type of solutionthat only addresses the tip of the ice-

berg. They will hardly make a dent,and we are very unlikely to see a new

type of clinker that is really going toreplace Portland cement by more than

1 or 2 percent.

Q:But you are not saying that noth-

ing can be done about the CO2emis-

sions of concrete production, right?

A:Absolutely not. There is a lotthat we can do, even with what might

appear to be small gains. For example,if we could even save 5 or 10 percent

CO2on every meter of concrete, it isorders of magnitude more important.

In fact, a 10-percent saving in the CO2

associated with a cubic meter of con-

crete, which is eminently doable, wouldbe equivalent to removing all the CO

2

emissions associated with steel produc-tion. That shows how much impact we

can have by research to increase thesustainability of cement and concrete.

Q:Can you explain a little moreabout your earlier comments about

cement composition having to belinked to available resources?

A:Sure. Only eight elementsoxy-gen, silicon, aluminum, iron, calcium,

sodium, potassium and magnesiummake up 98 percent of Earths crust.

Thus, we can forget about makingcement out of the other elements that

make up the 2 percent. We are forcedto look at these eight elements.

Of course, what wed like to do is to

reduce the amount of calcium because

calcium more or less correlates exactlywith amount of CO

2, because the cal-

cium oxide comes with the decomposi-

tion of calcium carbonate. In fact, thislimited range of choices is in many

ways an advantage, because we alreadyknow all the phases that form from

these elements and we can systemati-cally evaluate all possible solutions.

The way this has been pursued overthe past 20 or 30 years is first of all

process optimization. Its worth noting

the process of making cement is veryclose to the optimum, which you candetermine from making thermodynamic

calculations. In fact, the production isat about 80 percent of theoretical effi-

ciency and that is extremely good.Also, the cement kiln is very ver-

satile and can accept a wide range offuels. Many plants operate with more

than 80 percent of their fuel comingfrom waste sources, so we are efficiently

using the calorific value of wastes andalso efficiently decomposing toxic

(organic) materials because of the high

(Credit:KarenScrivener.)

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flame temperature (2,000C).

One of the directions going on nowto make reductions in CO

2is to reduce

the clinker factor. This means, insteadof making cement out of grinding clin-

ker and gypsum, we add more and more

of what are known as supplementarycementitious materials. These are oftenbyproducts or waste products from other

industries, such as fine limestone, flyash, blast-furnace slag, silica flume and

natural pozzolans.Now, this has been a very good

and successful strategy. So, at leastin Europe over the past 20 years or

so, manufacturers have reduced theamount of clinker in their cements

down to below 75 percent in preblend-

ed cements. In other words, they suc-cessfully substitute 25 percent of clinkerwith other materials.

Q:What about in the US?A:The US goes against this trend,

in a sense, because the nation uses alow amount of preblended cements.

Instead, SCMs are added at the stageof the concrete mixer. This is not the

best practice because it is not as wellcontrolled as production is at a cement

plant. This can lead to problems. But,

the overall trend is the same.Q:So is expanding the use of these

SCMs the best strategy going forward?A:This is quite a difficult strategy,

because if you look at the amount ofsupplementary materials available, we

see that it is totally dwarfed by theamount of cement produced. Even fly

ashweve all heard about fly ash, andit is probably the most widely avail-

able SCMis produced in very smallquantities. There simply isnt enough

fly ash worldwide to replace cement inany big amount. And, if we look into

where huge demand is going to be com-ing from, it is going to be coming from

underdeveloped countries that lacklarge amounts of slag and fly ash.

Q:So where are SCMs going tocome from?

A:I think we see more and morelimestone used, and also are going to

see more calcined clays and pozzolans.But, at the end of the day, what this

means is that we are going to see a verydiverse range of cements. Cements are

going to get more and more diverse

and more and more complicated,because there is no one single answer.

But, if we pursue all of these possiblesustainability routes in parallel, then I

think we have a chance to bring downthe CO

2emissions associated with con-

crete.Sustainability can come only from a

vastly and increasingly diverse rate ofuse of cementitious materials, includ-

ing SCMs, which are adapted to locallyavailable materials. In order to be able

to do this, we have to provide end userswith understanding and relevant per-

formance tests for them to have confi-dence in these solutions.

Put another way, what we reallywant to be able to do is to have the

composition of our materialsthecements, the SCMsand know how

they are mixed, the time of curing,temperature, relative humidity, etc.,

and from this to predict performance.

Performance can be on many differentlevels. Short-term performance likethe time it takes to initially set can be

quite easy to measure and predict inthe laboratory. But, when it comes to

properties, such as durabilitywherewe expect structures to last 4050 years

with little maintenanceit is not pos-sible to measure them in the lab.

Therefore, we have to go to anapproach based on mechanisms, par-

ticularly on microstructure. In fact, we

should be able to predict microstruc-

ture, based on thermodynamics and

kinetics. And, in predicting microstruc-ture, modeling will play a very impor-

tant role, because the models can helpus pull all of this complex information

together and have it make sense.In terms of thermodynamics, we

have about 90 percent of what we need.On kinetics, we have more work to do,

but progress is now very rapid.Q:Can you mention more about

some of the CO2

-saving materials that

might be used?A:If we think in terms of miner-

als that will hydrate that will reallysave CO

2, there are certainly calcium

aluminate and calcium sulfoaluminate(the mineral name is yeelimite). These

have much lower CO2emissions, about

40 percent less. They are also formed at

lower temperatures, and they are easierto grind. So, here, you can get net CO

2

savings. But, even so, many of thesetypes of cements currently being studied

give only an overall savings of 2030percent. But, say, if you are going to put

30-percent fly ash in Portland cement,you are back to the same levels again.

Really, it is important to startmaking comparisons not to Portland

cement but to present-day blendedcements, which may contain only

7080-percent clinker.But, I think the way it is really going

to go is to use calcined clay, becausewe have almost unlimited amounts of

clay. We have had very exciting results

(Credit:KarenScrivener.)

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Straight talk with Karen Scrivener on cements, CO2and sustainable development

with calcined clay. We have a program

in Cuba where we have shown thatyou can use low-grade clay. Weve be

able to show that you can take claythat contains only 30-percent kaolinite

and make a blend where you replace 30

percent of the cement and can get thesame strength as pure-Portland refer-

ence after three days. And, if we makea coupled substitution of calcined clay

plus limestone, then we can substitute60 percent and still get 90 percent of

the strength in seven days.This shows there are a lot of other

routes. We have got to stop thinkingjust in terms of slag and fly ash. I am

guilty of that myself. We get stuck onslag because its a homogeneous mate-

rial that is easy to study, but slag isntgoing to be that important in further

reducing CO2, because there is so little

of it available. Of course, where it is

available, you can use it at very highreplacement rates, but that availability

is very localized. And, in the long term,people are going to stop making iron in

blast furnaces, because that also con-tributes to CO

2emissions.

Q:Your talk at the cements meet-ing last year was on microstructure and

modeling hydration kinetics. Can youbriefly explain what this is about, and

how it ties into your work with theNanocem consortium?

A:What we really need to do is to

know how the microstructure of con-crete is forming. We have this rather

miraculous materialif you think about

it, you just mix in water and leave it atroom temperature and it makes a hard

materialbut we dont actually under-stand well what determines those pro-

cesses. I think we are making very rapidadvances, certainly more advances in

the past five years than in the previous

50 years. This is what we are doing inmy lab and where we are creating thesynergy in Europe of having this net-

work of laboratories working togetheron these problems. When we work

together and we have all of the compe-tencies tackling the same problems, we

can go much faster.We are also creating this environ-

ment where the industry is pleased toinvest in this fundamental work. This

industry has been considered low-tech

because the science is pretty compli-cated, and no one company has theresources to change the situation.

So, we bring the companies togetherin the Nanocem network, where we

have five of the worlds top six cementcompanies, including LeFarge, Cemex

and Heidelberg, who are responsiblefor 50 percent of the cement produc-

tion outside of China. And, if each ofthem is paying only for part of it, then

together they have a global pool that

can underwrite part of this research.

In all, there are 11 industrial partnersand 22 academic partners in Nanocem,

and, by building this consortium, we arebringing about a paradigm change in

what type of research can be done.Q:Are there specific research goals

for Nanocem?A:Yes. The first thing we want to

predict with our research is how thesematerials harden. The second stage of

the process, equally important, is pre-

dicting how the material will performover the lifetime of the building or

the structure in which the concrete isused. Typically we are talking about

lifespans of 50100 years. Field researchisnt very practical, so we have to use

the predictive methods coming out of

materials science.We now have, for example, fund-

ing from the European Community

for 15 linked PhD projects that arejointly addressing the question of water

transport, which is the central processby which all degradation mechanisms

occur. The idea is to understand thismechanism and how it is affected by

different cement types, such as thosemade with the new low-CO

2materials.

When we achieve this understanding,

we are really changing the whole basison which we can predict its perfor-mance.

Q:Are some people surprised by theresponsiveness of the industry?

A:Well, business is business, as theysay, for the cement and concrete com-

panies, but they really want to be in asustainable business, and they are prob-

ably harmed because they dont havethe public relations budgets of, say, the

oil industry. But, we have to give them

credit for the fact that cement pricesare fairly steady and still incrediblycheap. You can still get a ton of cement

for around e100. These companies arenot making huge profits, and they are

constrained about what they can indi-vidually do. But my experience is that

the management of these companies

has a real interest in having a sustain-able society.

For more information on Nanocem,

visit www.nanocem.org.n

(Cre

dit:KarenScrivener.)